Rubber (and/or rubber-like) connectors are utilized to provide a water-tight seal between an opening in a manhole assembly, for example, and a pipe extending into the opening. U.S. Pat. No. 4,159,829 assigned to the assignee of the present invention discloses a conventional bi-directional connector formed from an extrusion having a hollow pear-shaped head portion integrally joined to a T-shaped anchoring flange. A connector ring is formed by cutting an extruded sectional length and curling it to form a substantially tight-cylinder configuration with the mating edges being joined. The pear-shaped head portion deflects from a radially inwardly extending orientation upon insertion of a pipe. The resiliency of the head portion is improved by providing a single cavity to obtain moderate sealing pressure.
U.S. Pat. No. 4,508,355, also assigned to the assignee of the present invention constitutes an improvement over U.S. Pat. No. 4,159,829 by providing a gasket of similar shape having a plurality of internal cavities extending longitudinally through the head portion to provide the desired resiliency while at the same time providing improved stability of the gasket, yielding a stronger, more uniform seal about the exterior of the pipe extending therethrough, including portions of the pipe surface which may be significantly out-of-round.
The above designs have the disadvantage of providing a water-tight seal which weakens as water pressure applied to the gasket increases and which have very narrow tolerance limits with regard to the range of pipe outer diameter that can be accepted by a gasket thereby greatly increasing the number of gaskets required to cover a large range of pipe outer diameters, typically from 4" to 84".
The assignee of the present invention has further developed a gasket which is described in U.S. Pat. No. Re. 34,787, which gasket provides water pockets that enhance the water-tight seal with increasing pressure. The gasket described therein has a T-shaped anchoring portion and a substantially A-shaped or pear-shaped pipe engaging head portion similar to those found in conventional gaskets. However, the head portion of the improved gasket is provided with a recess near its wide end defining a pair of legs extending away from the head portion which act as water seal flaps. The midpoint of the recess is joined to the anchoring portion by an integral connecting web having a thickness which is significantly reduced relative to the thickness of the adjacent anchoring portion to facilitate bending of the web and hence the gasket.
A connecting web cooperates with the legs and recess to form a pair of water pockets, one of which becomes active dependent upon the direction which the gasket is deflected, to provide a water-tight seal which seal increases in effectiveness with increasing water pressure imposed upon the gasket.
The water pockets in the gasket disclosed in U.S. Pat. No. Re 34,787 has been found to have certain disadvantages which include the tendency of the water pocket to flip over during insertion of a pipe. In addition, the connecting web has been found to significantly reduce the compression of the gasket against the pipe.
The gaskets of the type described in U.S. Pat. No. Re 34,787 are normally extruded and then cut to size to form a gasket of the desired diameter. During the extrusion process, the gaskets are extruded so that the axis of symmetry of the extrusion is horizontally aligned as the extrusion leaves the die in order for the extrusion to be placed on its side upon a conveyor which carries the extrusion through a curing medium. The geometry of the extrusion is such that the imbedment portion of the extrusion and specifically the web connecting the imbedment portion to the head portion deviates from the normal line of symmetry due to the fact that the extrusion is not able to retain the desired symmetrical orientation because the extrusion is sufficiently soft prior to curing, so that a bend developed as the extrusion is conveyed through the curing region becomes fixed as a result of the curing operation. Thus, when the extrusion is cured, the connecting web and embedment portion deviates from the desired symmetry and becomes misaligned within the cast member into which it is embedded thereby significantly reducing and weakening the ability of the cast member to properly retain the gasket embedded within the cast member.
The design of the water pockets in the gasket disclosed in U.S. Pat. No. Re 34,787 further complicate the joining of the gasket ends necessitating the employment of a plurality of inserts in order to assure proper alignment of the ends of the extruded section being joined thereby complicating the joining operation and degrading the accuracy of the alignment of the end sections of the extrusion being joined, especially in the regions of the water pocket, as well as requiring additional pin-like joining members inserted into adjacent ends of the cut length of the extruded member to assure that said ends are properly joined.
It has been found that the embedment portion of the gasket undergoes some stretching and hence thinning as a pipe is inserted into the gasket, which is disadvantageous as it severely reduces the ability to prevent infiltration of water around the waterstop, especially in drycast assemblies.